Conventionally, physicochemical signals emitted in accordance with the activities of biological samples are taken into a measurement apparatus and measured as electrical signals, or as digital signals, such as the fluorescence intensity signals that are emitted from the biological sample when an indicator is incorporated therein. For example, when measuring the channel activation of a cell at the single channel level, an electrophysiology measurement apparatus provided with a microelectrode probe, such as a patch clamp, and an exclusive control device is used to obtain digital signals showing the quantity of electricity passing through the channel. The obtained digital signals are used to calculate the opening/closing periods, timing and frequency of the channel for measuring channel activation.
The patch clamp method employs a micro portion (patch) of a cell membrane attached to a tip of a micropipette so that ion transport via a single channel protein molecule can be electrically recorded with the microelectrode probe. Among cell biology techniques, the patch clamp method is one of the few methods that permit the real-time examination of the functions of a single protein molecule (e.g., “Molecular Biology of the Cell”, 3rd edition, published by Garland Publishing Inc., New York, 1994, Japanese translation by Keiko NAKAMURA et al., pages 181 to 182, published in 1995 by Kyoiku Sha).
A fluorescent dye method is used for measuring the electrical activity of a cell in combination of an image processor and a luminous indicator or a fluorochrome that emits light depending on the concentration variations in a specified ion. For example, the ion mobility within a cell is monitored based on the fluorescence images of a cell taken by a CCD camera. According to the fluorescent dye method, the ion channel activation of an entire cell is generally determined by measuring the quantity of ions flowing into the cell by the fluorescence measurement method.
More specifically, the patch clamp method requires specialized techniques for preparing and handling a micropipette and takes a lot of time to measure one sample. Therefore, the patch clamp method is not suitable for the high-speed screening of various types of drug candidate compounds. In contrast, the fluorescent dye method permits the high-speed screening of various types of drug candidate compounds. However, the fluorescent dye method requires the step of dyeing the cell, which raises the problems of the high background caused by the dyestuff and the decolorization of the dyed cell with the passage of time, resulting in a lowered S/N ratio at measurement.
Methods for observing electrical and chemical variations in biological samples are disclosed in the prior art references of U.S. Pat. Nos. 2,949,845, 5,810,725, 5,563,067 and 5,187,069, Japanese Unexamined Patent Publication No. 1997-827318, and International Publication Nos. WO 01/25769, WO 98/54294, WO 99/66329 and WO 99/31503.
U.S. Pat. Nos. 2,949,845, 5,810,725 and 5,563,067 and Japanese Unexamined Patent Publication No. 1997-827318 disclose an integrated complex electrode and a measurement system using the same which are characterized by forming microelectrodes on a glass substrate using a photolithographic technique so as to extracellularly monitor the electrical changes of a cell with a multipoint.
International Publication No. WO 01/25769 discloses forming perforations on an insulating substrate, and arranging biological samples such as cells or the like containing ion channels at the perforations, so that a giga-seal is formed on the cell or the like and the insulating substrate surface. The thus configured substrate uses reference electrodes and measurement electrodes that are disposed at two areas separated by the giga-seal to measure the current that is generated when the ions pass through the ion channels.
U.S. Pat. No. 5,187,069 discloses a device which culture cells on an electrode and measures impedance changes to monitor cell proliferation.
International Publication No. WO 98/54294 discloses a device which causes a cell to adhere to a planar electrode for measuring electrical signals.
International Publication No. WO 99/66329 discloses a device for monitoring the activities of a cell on a porous material according to variations in resistance and impedance, and an assay method using the device.
International Publication No. WO. 99/31503 discloses a method using a substrate provided with perforations wherein a patch clamp is formed by trapping cells onto the perforations for use in measuring current variations.
Other prior arts of the present invention include Japanese Unexamined Patent Publication Nos. 1999-326166, 1993-157728 and 1987-73152.